Steering wheel position sensors are employed by vehicle controllers for determining the angular position and rotational speed of the steering wheel. Steering wheel angle and speed information have application to various vehicle systems. For example, it has been proposed to utilize vehicle steering wheel angle for anti-lock braking and active suspension systems for enabling such control systems to alter their operation in response to vehicle turning.
Magnetic position sensors are commonly used as steering wheel position sensors. They require cooperating elements including a magnetic field, a movable target wheel and one or more stationary sensors. Movement of the target wheel produces variations in the flux density of the magnetic field as detected by the sensor.
Target wheels formed of ferromagnetic material, usually soft steel, are not capable of producing the required magnetic field. Therefore, a separate biasing magnet is required to generate the magnetic field through which the target wheel is rotated. Changes in the magnetic field caused by movement of the target wheel are sensed by a Hall effect or magnetoresistive sensor, providing an indication of angular movement of the target wheel.
It is desirable to have a simpler configuration of cooperating elements whereby the required variable magnetic field is produced by the target wheel, thereby eliminating the need for a separate biasing magnet. Movement of the target wheel with respect to the stationary sensor causes variations in the magnetic field density as detected by the sensor. By eliminating the need for a separate biasing magnet, the size and cost of the sensing apparatus can be substantially reduced. The magnetized target wheel can also produce larger signals with higher spatial resolution compared to a ferromagnetic target wheel with a bias magnet.